Self-assembly of tunable protein suprastructures from recombinant oleosin

Injectable network biomaterials via molecular or colloidal self-assembly

Self-assembly is a powerful tool to create functional materials. A specific application for which self-assembled materials are ideally suited is in creating injectable biomaterials. Contrasting with traditional biomaterials that are implanted through surgical means, injecting biomaterials through the skin offers numerous advantages, expanding the scope and impact for biomaterials in medicine. In particular, self-assembled biomaterials prepared from molecular or colloidal interactions have been frequently explored. The strategies to create these materials are varied, taking advantage of engineered oligopeptides, proteins, and nanoparticles as well as affinity-mediated crosslinking of synthetic precursors. Self-assembled materials typically facilitate injectability through two different mechanisms: i) in situ self-assembly, whereby materials would be administered in a monomeric or oligomeric form and self-assemble in response to some physiologic stimulus, or ii) self-assembled materials that, by virtue of their dynamic, non-covalent interactions, shear-thin to facilitate flow within a syringe and subsequently self-heal into its reassembled material form at the injection site. Indeed, many classes of materials are capable of being injected using a combination of these two mechanisms. Particular utility has been noted for self-assembled biomaterials in the context of tissue engineering, regenerative medicine, drug delivery, and immunoengineering. Given the controlled and multifunctional nature of many self-assembled materials demonstrated to date, we project a future where injectable self-assembled biomaterials afford improved practice in advancing healthcare.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.

Engineering Globular Protein Vesicles through Tunable Self-Assembly of Recombinant Fusion Proteins

Vesicles assembled from folded, globular proteins have potential for functions different from traditional lipid or polymeric vesicles. However, they also present challenges in understanding the assembly process and controlling vesicle properties. From detailed investigation of the assembly behavior of recombinant fusion proteins, this work reports a simple strategy to engineer protein vesicles containing functional, globular domains. This is achieved through tunable self-assembly of recombinant globular fusion proteins containing leucine zippers and elastin-like polypeptides. The fusion proteins form complexes in solution via high affinity binding of the zippers, and transition through dynamic coacervates to stable hollow vesicles upon warming. The thermal driving force, which can be tuned by protein concentration or temperature, controls both vesicle size and whether vesicles are single or bi-layered. These results provide critical information to engineer globular protein vesicles via self-assembly with desired size and membrane structure.

Efficient Way to Generate Protein-Based Nanoparticles by in-Situ Photoinitiated Polymerization-Induced Self-Assembly

Protein-based nanoparticles with tailored properties by using different functional proteins as building blocks have many actual and potential applications in biomedicine, biotechnology, and nanotechnology. In this study, we demonstrated a facile and efficient way to synthesize protein-based nanoparticles by taking advantage of photoinitiated reversible addition-fragmentation chain transfer (RAFT) polymerization-induced self-assembly by using multi-RAFT modified bovine serum albumin (BSA) as a macro-RAFT agent. The growth of the PHPMA chains results in the increase of the hydrophobicity of the star BSA-PHPMA conjugates, and when reaching the critical aggregation concentration in aqueous solution, they will aggregate into nanoparticles via the hydrophobic interaction of PHPMA. The generated nanoparticles also showed excellent encapsulation ability toward both hydrophobic and hydrophilic components, and as a proof of concept, after loading cancer drug DOX or biomacromolecule DNA, the protease-mediated release of the encapsulants was demonstrated. It is anticipated that the described method may open up new opportunities for designing a variety of protein-polymer self-assembled nanostructures tailored to specific applications.

Designing Smart Materials with Recombinant Proteins

Recombinant protein design allows modular protein domains with different functionalities and responsive behaviors to be easily combined. Inclusion of these protein domains can enable recombinant proteins to have complex responses to their environment (e.g., temperature-triggered aggregation followed by enzyme-mediated cleavage for drug delivery or pH-triggered conformational change and self-assembly leading to structural stabilization by adjacent complementary residues). These "smart" behaviors can be tuned by amino acid identity and sequence, chemical modifications, and addition of other components. A wide variety of domains and peptides have smart behavior. This review focuses on protein designs for self-assembly or conformational changes due to stimuli such as shifts in temperature or pH.

Pure Protein Bilayers and Vesicles from Native Fungal Hydrophobins

Pure protein bilayers and vesicles are formed using the native, fungal hydrophobin HFBI. Bilayers with hydrophobic (red) and hydrophilic (blue) core are produced and, depending on the type of core, vesicles in water, oily media, and even in air can be created using microfluidic jetting. Vesicles in water are even able to incorporate functional gramicidin A pores.

Self-Assembled Materials Made from Functional Recombinant Proteins

Proteins are potent molecules that can be used as therapeutics, sensors, and biocatalysts with many advantages over small-molecule counterparts due to the specificity of their activity based on their amino acid sequence and folded three-dimensional structure. However, they also have significant limitations in their stability, localization, and recovery when used in soluble form. These opportunities and challenges have motivated the creation of materials from such functional proteins in order to protect and present them in a way that enhances their function. We have designed functional recombinant fusion proteins capable of self-assembling into materials with unique structures that maintain or improve the functionality of the protein. Fusion of either a functional protein or an assembly domain to a leucine zipper domain makes the materials design strategy modular, based on the high affinity between leucine zippers. The self-assembly domains, including elastin-like polypeptides (ELPs) and defined-sequence random coil polypeptides, can be fused with a leucine zipper motif in order to promote assembly of the fusion proteins into larger structures upon specific stimuli such as temperature and ionic strength. Fusion of other functional domains with the counterpart leucine zipper motif endows the self-assembled materials with protein-specific functions such as fluorescence or catalytic activity. In this Account, we describe several examples of materials assembled from functional fusion proteins as well as the structural characterization, functionality, and understanding of the assembly mechanism. The first example is zipper fusion proteins containing ELPs that assemble into particles when introduced to a model extracellular matrix and subsequently disassemble over time to release the functional protein for drug delivery applications. Under different conditions, the same fusion proteins can self-assemble into hollow vesicles. The vesicles display a functional protein on the surface and can also carry protein, small-molecule, or nanoparticle cargo in the vesicle lumen. To create a material with a more complex hierarchical structure, we combined calcium phosphate with zipper fusion proteins containing random coil polypeptides to produce hybrid protein-inorganic supraparticles with high surface area and porous structure. The use of a functional enzyme created supraparticles with the ability to degrade inflammatory cytokines. Our characterization of these protein materials revealed that the molecular interactions are complex because of the large size of the protein building blocks, their folded structures, and the number of potential interactions including hydrophobic interactions, electrostatic interactions, van der Waals forces, and specific affinity-based interactions. It is difficult or even impossible to predict the structures a priori. However, once the basic assembly principles are understood, there is opportunity to tune the material properties, such as size, through control of the self-assembly conditions. Our future efforts on the fundamental side will focus on identifying the phase space of self-assembly of these fusion proteins and additional experimental levers with which to control and tune the resulting materials. On the application side, we are investigating an array of different functional proteins to expand the use of these structures in both therapeutic protein delivery and biocatalysis.

Computationally designed peptides for self-assembly of nanostructured lattices

Folded peptides present complex exterior surfaces specified by their amino acid sequences, and the control of these surfaces offers high-precision routes to self-assembling materials. The complexity of peptide structure and the subtlety of noncovalent interactions make the design of predetermined nanostructures difficult. Computational methods can facilitate this design and are used here to determine 29-residue peptides that form tetrahelical bundles that, in turn, serve as building blocks for lattice-forming materials. Four distinct assemblies were engineered. Peptide bundle exterior amino acids were designed in the context of three different interbundle lattices in addition to one design to produce bundles isolated in solution. Solution assembly produced three different types of lattice-forming materials that exhibited varying degrees of agreement with the chosen lattices used in the design of each sequence. Transmission electron microscopy revealed the nanostructure of the sheetlike nanomaterials. In contrast, the peptide sequence designed to form isolated, soluble, tetrameric bundles remained dispersed and did not form any higher-order assembled nanostructure. Small-angle neutron scattering confirmed the formation of soluble bundles with the designed size. In the lattice-forming nanostructures, the solution assembly process is robust with respect to variation of solution conditions (pH and temperature) and covalent modification of the computationally designed peptides. Solution conditions can be used to control micrometer-scale morphology of the assemblies. The findings illustrate that, with careful control of molecular structure and solution conditions, a single peptide motif can be versatile enough to yield a wide range of self-assembled lattice morphologies across many length scales (1 to 1000 nm).

Programmable Modulation of Membrane Permeability of Proteinosome upon Multiple Stimuli Responses

Membrane permeability is a necessary and overarching attribute for all the hollow microcompartments toward the application as nanoreactors or artificial cells. Differing from the widely reported various stimuli models, in this study we describe a way to generate a multistimuli proteinosome capable of being triggered in sequence of temperature, redox species, and pH, thus, showing a continuous modulation on the membrane permeability. Studies showed that the molecular weight cutoff of the constructed proteinosome membrane could be continuously turned up from 78 to 102 kDa and to 142 kDa, and then turned down to 35.2 kDa upon different stimuli. As a proof of concept, such continuous modulated behavior allows a well-controlled programmed release upon the encapsulation of a FITC-labeled dextran into proteinosomes. It is anticipated that such designed proteinosomes equipped with programmed modulation of membrane permeability are promising candidates for the further development of artificial model design, such as cellular communication or metabolism in which stuff exchange is required to support in situ procedures.

Tuning the Mechanical Properties of Recombinant Protein-Stabilized Gas Bubbles Using Triblock Copolymers

Gas bubbles enhance contrast in ultrasound sonography and can also carry and deliver therapeutic agents. The mechanical properties of the bubble shell play a critical role in determining the physical response of gas bubbles under ultrasound insonation. Currently, few methods allow for tailoring of the mechanical properties of the stabilizing layers of gas bubbles. Here, we demonstrate that blending of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic triblock copolymer with a recombinant protein, oleosin, enables the tuning of the mechanical properties of the bubble stabilizing layer. The areal expansion modulus of gas bubbles, as determined by micropipette aspiration, depends on the structure as well as the concentration of PEO-PPO-PEO triblock copolymers. We believe our method of using a mixture of PEO-PPO-PEO and oleosin can potentially lead to the formation of microbubbles with stabilizing shells that can be functionalized and tailored for specific applications in ultrasound imaging and therapy.

Soft matter food physics--the physics of food and cooking

This review discusses the (soft matter) physics of food. Although food is generally not considered as a typical model system for fundamental (soft matter) physics, a number of basic principles can be found in the interplay between the basic components of foods, water, oil/fat, proteins and carbohydrates. The review starts with the introduction and behavior of food-relevant molecules and discusses food-relevant properties and applications from their fundamental (multiscale) behavior. Typical food aspects from 'hard matter systems', such as chocolates or crystalline fats, to 'soft matter' in emulsions, dough, pasta and meat are covered and can be explained on a molecular basis. An important conclusion is the point that the macroscopic properties and the perception are defined by the molecular interplay on all length and time scales.

Pathways to dewetting in hydrophobic confinement

Liquid water can become metastable with respect to its vapor in hydrophobic confinement. The resulting dewetting transitions are often impeded by large kinetic barriers. According to macroscopic theory, such barriers arise from the free energy required to nucleate a critical vapor tube that spans the region between two hydrophobic surfaces--tubes with smaller radii collapse, whereas larger ones grow to dry the entire confined region. Using extensive molecular simulations of water between two nanoscopic hydrophobic surfaces, in conjunction with advanced sampling techniques, here we show that for intersurface separations that thermodynamically favor dewetting, the barrier to dewetting does not correspond to the formation of a (classical) critical vapor tube. Instead, it corresponds to an abrupt transition from an isolated cavity adjacent to one of the confining surfaces to a gap-spanning vapor tube that is already larger than the critical vapor tube anticipated by macroscopic theory. Correspondingly, the barrier to dewetting is also smaller than the classical expectation. We show that the peculiar nature of water density fluctuations adjacent to extended hydrophobic surfaces--namely, the enhanced likelihood of observing low-density fluctuations relative to Gaussian statistics--facilitates this nonclassical behavior. By stabilizing isolated cavities relative to vapor tubes, enhanced water density fluctuations thus stabilize novel pathways, which circumvent the classical barriers and offer diminished resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie-Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly.

Directional self-assembly of ligand-stabilized gold nanoparticles into hollow vesicles through dynamic ligand rearrangement

Here we report a novel approach to prepare all-nanoparticle vesicles using ligand-stabilized gold particles as a building block. Hydroxyalkyl-terminated gold nanoparticles were spontaneously organized into well-defined hollow vesicle-like assemblies in water without any template. The unusual anisotropic self-assembly was attributed to the ligand rearrangement on nanoparticles, which leads to increased hydroxyl group density at the nanoparticle/water interface. One-dimensional strings were formed instead of vesicles with increasing surface ligand density, which supports the hypothesis. The size and the wall thickness of vesicles were controlled by adjusting the concentration of nanoparticles or by adding extra surfactants. The work presented here highlights the dynamic nature of surface ligands on gold particles and demonstrates that the combination of ligand rearrangement and the hydrophobic effect can be used as a versatile tool for anisotropic self-assembly of nanoparticles.

New frontiers for encapsulation in the chemical industry

Encapsulation of actives comprises an area of exploration undergoing rapid growth in both academic and industrial research settings. Encapsulation processes are employed as a part of product synthesis processes for improved efficiency, enhanced stability, active ingredient compatibility, increased safety, targeted delivery, and novel performance of the end product. Such technical benefits enable producers to offer products with increased formulation complexity, access new markets, differentiate products, and improve compatibility and stability, while meeting consumer demands with improved performance, reduced costs, and new actives. In this review, we highlight several emerging academic areas of encapsulation that we believe have specific relevance to industrial formulation, with a focus on three primary areas: supramolecular encapsulation, aqueous self-assembled systems, and emulsion-based capsules. The goal of this review is to help identify the major challenges facing encapsulation technology adoption in the chemical industry, bringing focus and maximizing the potential value of ongoing research efforts.

Superparamagnetic iron oxide nanoparticle micelles stabilized by recombinant oleosin for targeted magnetic resonance imaging

Recombinant surfactants present a new platform for stabilizing and targeting nanoparticle imaging agents. Superparamagnetic iron oxide nanoparticle-loaded micelles for MRI contrast are stabilized by an engineered variant of the naturally occurring protein oleosin and targeted using a Her2/neu affibody-oleosin fusion. The recombinant oleosin platform allows simple targeting and the ability to easily swap the ligand for numerous targets.

Designer amphiphilic proteins as building blocks for the intracellular formation of organelle-like compartments

Nanoscale biological materials formed by the assembly of defined block-domain proteins control the formation of cellular compartments such as organelles. Here, we introduce an approach to intentionally 'program' the de novo synthesis and self-assembly of genetically encoded amphiphilic proteins to form cellular compartments, or organelles, in Escherichia coli. These proteins serve as building blocks for the formation of artificial compartments in vivo in a similar way to lipid-based organelles. We investigated the formation of these organelles using epifluorescence microscopy, total internal reflection fluorescence microscopy and transmission electron microscopy. The in vivo modification of these protein-based de novo organelles, by means of site-specific incorporation of unnatural amino acids, allows the introduction of artificial chemical functionalities. Co-localization of membrane proteins results in the formation of functionalized artificial organelles combining artificial and natural cellular function. Adding these protein structures to the cellular machinery may have consequences in nanobiotechnology, synthetic biology and materials science, including the constitution of artificial cells and bio-based metamaterials.

Zn2+ and Cu2+ induced nanosheets and nanotubes in six different lectins by TEM

Zn²⁺ and Cu²⁺ induced supramolecular assemblies of lectins resulted in the formation of nanosheets in case of Zn²⁺ and both nanosheets and nanotubes in case of Cu²⁺ having different features characteristic of the lectin and the metal ion present. These nanostructures are unprecedented and would lead to major advances in nanobiomaterial science.

Noncanonical self-assembly of highly asymmetric genetically encoded polypeptide amphiphiles into cylindrical micelles

Elastin-like polypeptides (ELPs) are a class of biopolymers consisting of the pentameric repeat (VPGαG)n based on the sequence of mammalian tropoelastin that display a thermally induced soluble-to-insoluble phase transition in aqueous solution. We have discovered a remarkably simple approach to driving the spontaneous self-assembly of high molecular weight ELPs into nanostructures by genetically fusing a short 1.5 kDa (XGy)z assembly domain to one end of the ELP. Classical theories of self-assembly based on the geometric mass balance of hydrophilic and hydrophobic block copolymers suggest that these highly asymmetric polypeptides should form spherical micelles. Surprisingly, when sufficiently hydrophobic amino acids (X) are presented in a periodic sequence such as (FGG)8 or (YG)8, these highly asymmetric polypeptides self-assemble into cylindrical micelles whose length can be tuned by the sequence of the morphogenic tag. These nanostructures were characterized by light scattering, tunable resistive pulse sensing, fluorescence spectrophotometry, and thermal turbidimetry, as well as by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). These short assembly domains provide a facile strategy to control the size, shape, and stability of stimuli responsive polypeptide nanostructures.

Recombinant protein-stabilized monodisperse microbubbles with tunable size using a valve-based microfluidic device

Microbubbles are used as contrast enhancing agents in ultrasound sonography and more recently have shown great potential as theranostic agents that enable both diagnostics and therapy. Conventional production methods lead to highly polydisperse microbubbles, which compromise the effectiveness of ultrasound imaging and therapy. Stabilizing microbubbles with surfactant molecules that can impart functionality and properties that are desirable for specific applications would enhance the utility of microbubbles. Here we generate monodisperse microbubbles with a large potential for functionalization by combining a microfluidic method and recombinant protein technology. Our microfluidic device uses an air-actuated membrane valve that enables production of monodisperse microbubbles with narrow size distribution. The size of microbubbles can be precisely tuned by dynamically changing the dimension of the channel using the valve. The microbubbles are stabilized by an amphiphilic protein, oleosin, which provides versatility in controlling the functionalization of microbubbles through recombinant biotechnology. We show that it is critical to control the composition of the stabilizing agents to enable formation of highly stable and monodisperse microbubbles that are echogenic under ultrasound insonation. Our protein-shelled microbubbles based on the combination of microfluidic generation and recombinant protein technology provide a promising platform for ultrasound-related applications.

Controlled nanometric fibers of self-assembled designed protein scaffolds

The use of biological molecules as platforms for templating and nanofabrication is an emerging field. Here, we use designed protein building blocks based on small repetitive units (consensus tetratricopeptide repeat - CTPR) to generate fibrillar linear nanostructures by controlling the self-assembly properties of the units. We fully characterize the kinetics and thermodynamics of the assembly and describe the polymerization process by a simple model that captures the features of the structures formed under defined conditions. This work, together with previously established functionalization potential, sets up the basis for the application of these blocks in the fabrication and templating of complex hybrid nanostructures.

Spherical micelles assembled from variants of recombinant oleosin

An emerging field in biomaterials is the creation and engineering of protein surfactants made by recombinant biotechnology. Protein surfactants made by recombinant biotechnology allow for complete control of the molecular weight and chemical sequence of the surfactant. The proteins are monodisperse in molecular weight, and functionalization with bioactive amino acid sequences is straightforwardly achieved through genetic engineering. We modified the naturally occurring amphiphilic plant protein oleosin by truncating a large portion of its central hydrophobic block, creating a soluble triblock surfactant. Additional variants were constructed to eliminate secondary structure and create ionic surfactants. Variants of oleosin self-assembled into spherical micelles with a diameter of ∼21 nm at concentrations above the critical micelle concentration (cmc). We found that the cmc could be manipulated through changes in the protein backbone and was correlated with changes in the protein secondary structure. Micelle size and shape are characterized with dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). Micelles were functionalized with the integrin-binding domain, RGDS, leading to a 2.9-fold increase in uptake in Ovcar-5 cells after 12 h. Oleosin surfactants present a promising platform for micellar assembly because of the ability to precisely modify the protein backbone through molecular biology, allowing for the control over the cmc and the addition of functional domains into the material.

Integration of surface-active, periodically sequenced peptides into lipid-based microbubbles

The development of microbubbles toward functional, "theranostic" particles requires the incorporation of constituents with high binding specificity and therapeutic efficacy. Integrating peptides or proteins into the shell of lipid-based microbubbles can provide a means to access both receptor-ligand interactions and therapeutic properties. Simultaneously, peptides or proteins can define the characteristic monolayer mechanics of lipid bubbles and eliminate the need for post-bubble generation modification. The ability to engineer peptide sequences de novo that effectively partition into the bubble monolayer remains parametrically daunting. This work contributes to this effort using two simple amphipathic helical peptides that examine the role of local electrostatics and secondary structure. The two periodically sequenced peptides both have three positive charges, but peptide "K-2.5" spaces those charges 2.5 amino acids apart, while peptide "K-6.0" spaces the charges six amino acids apart. Size populations were determined for bubbles containing each peptide species using light scattering, and a quantitative method was developed to clearly define the fraction of peptides binding onto the microbubble monolayer. The impact of both the initial peptide concentration and the zwitterionic:anionic lipid ratio on peptide binding was also evaluated. Our results indicate that the lipid ratio affected only K-6.0 binding, which appears to be an outcome of the greater ensemble average α-helical population of the K-6.0. These findings provide further insights into the role of charge separation on peptide secondary structure, establishing a simple design metric for peptide binding onto microbubble systems.

An amphipathic alpha-helical peptide from apolipoprotein A1 stabilizes protein polymer vesicles

L4F, an alpha helical peptide inspired by the lipid-binding domain of the ApoA1 protein, has potential applications in the reduction of inflammation involved with cardiovascular disease as well as an antioxidant effect that inhibits liver fibrosis. In addition to its biological activity, amphipathic peptides such as L4F are likely candidates to direct the molecular assembly of peptide nanostructures. Here we describe the stabilization of the amphipathic L4F peptide through fusion to a high molecular weight protein polymer. Comprised of multiple pentameric repeats, elastin-like polypeptides (ELPs) are biodegradable protein polymers inspired from the human gene for tropoelastin. Dynamic light scattering confirmed that the fusion peptide forms nanoparticles with a hydrodynamic radius of approximately 50nm, which is unexpectedly above that observed for the free ELP (~5.1nm). To further investigate their morphology, conventional and cryogenic transmission electron microscopy were used to reveal that they are unilamellar vesicles. On average, these vesicles are 49nm in radius with lamellae 8nm in thickness. To evaluate their therapeutic potential, the L4F nanoparticles were incubated with hepatic stellate cells. Stellate cell activation leads to hepatic fibrosis; furthermore, their activation is suppressed by anti-oxidant activity of ApoA1 mimetic peptides. Consistent with this observation, L4F nanoparticles were found to suppress hepatic stellate cell activation in vitro. To evaluate the in vivo potential for these nanostructures, their plasma pharmacokinetics were evaluated in rats. Despite the assembly of nanostructures, both free L4F and L4F nanoparticles exhibited similar half-lives of approximately 1h in plasma. This is the first study reporting the stabilization of peptide-based vesicles using ApoA1 mimetic peptides fused to a protein polymer; furthermore, this platform for peptide-vesicle assembly may have utility in the design of biodegradable nanostructures.

Unique crystal structure of a novel surfactant protein from the foam nest of the frog Leptodactylus vastus

Breeding by releasing eggs into stable biofoams ("foam nests") is a peculiar reproduction mode within anurans, fish, and tunicates; not much is known regarding the biochemistry or molecular mechanisms involved. Lv-ranaspumin (Lv-RSN-1) is the predominant protein from the foam nest of the frog Leptodactylus vastus. This protein shows natural surfactant activity, which is assumed to be crucial for stabilizing foam nests. We elucidated the amino acid sequence of Lv-RSN-1 by de novo sequencing with mass-spectrometry and determined the high-resolution X-ray structure of the protein. It has a unique fold mainly composed of a bundle of 11 α-helices and two small antiparallel β-strands. Lv-RSN-1 has a surface rich in hydrophilic residues and a lipophilic cavity in the region of the antiparallel β-sheet. It possesses intrinsic surface-active properties, reducing the surface tension of water from 73 to 61 mN m(-1) (15 μg mL(-1)). Lv-RSN-1 belongs to a new class of surfactants proteins for which little has been reported regarding structure or function.

Thermosensitive AB4 four-armed star PNIPAM-b-HTPB multiblock copolymer micelles for camptothecin drug release

Thermo-sensitive poly(N-isoproplacrylamide)m-block-hydroxyl-terminated polybutadiene-block-poly(N-isoproplacrylamide)m (PNIPAMm-b-HTPB-b-PNIPAMm, m = 1 or 2) block copolymers, AB4 four-armed star multiblock and linear triblock copolymers, were synthesized by ATRP with HTPB as central blocks, and characterization was performed by (1)H NMR, Fourier transform infrared, and size exclusion chromatography. The multiblock copolymers could spontaneously assemble into more regular spherical core-shell nanoscale micelles than the linear triblock copolymer. The physicochemical properties were detected by a surface tension, nanoparticle analyzer, transmission electron microscope (TEM), dynamic light scattering, and UV-vis measurements. The multiblock copolymer micelles had lower critical micelle concentration than the linear counterpart, TEM size from 100 to 120 nm, and the hydrodynamic diameters below 150 nm. The micelles exhibited thermo-dependent size change, with low critical solution temperature of about 33-35 °C. The characteristic parameters were affected by the composition ratios, length of PNIPAM blocks, and molecular architectures. The camptothecin release demonstrated that the drug release was thermo-responsive, accompanied by the temperature-induced structural changes of the micelles. MTT assays were performed to evaluate the biocompatibility or cytotoxicity of the prepared copolymer micelles.

Thermosensitive PNIPAM-b-HTPB block copolymer micelles: molecular architectures and camptothecin drug release

Two kinds of thermo-sensitive poly(N-isoproplacrylamide) (PNIPAM) block copolymers, AB4 four-armed star multiblock and linear triblock copolymers, were synthesized by ATRP with hydroxyl-terminated polybutadiene (HTPB) as central blocks, and characterization was performed by (1)H NMR, FT-IR and SEC. The multiblock copolymers could spontaneously assemble into more regular spherical core-shell nanoscale micelles than the linear triblock copolymer. The physicochemical properties were detected by a surface tension technique, nano particle analyzer, TEM, DLS and UV-vis measurements. The multiblock copolymer micelles had lower critical micelle concentration than the linear counterpart, TEM size from 100 to 120 nm and the hydrodynamic diameters below 150 nm. The micelles exhibited thermo-dependent size change, with low critical solution temperature about 33-35 °C. The characteristic parameters were affected by the composition ratios, length of PNIPAM blocks and molecular architectures. The camptothecin release demonstrated that the drug release was thermo-responsive, accompanied by the temperature-induced structural changes of the micelles. MTT assays were performed to evaluate the biocompatibility or cytotoxicity of the prepared copolymer micelles.

Polymersomes and Multicompartment Polymersomes Formed by the Interfacial Self-Assembly of Gold Nanoparticles and Amphiphilic Polymers

Here, we report the formation of polymer vesicles (polymersomes) uniformly decorated with gold nanoparticles (AuNPs) through the interfacial self-assembly of 11-mercapto-1-undecanol (MUL)-stabilized AuNPs and two prototypical amphiphilic polymers (i.e., polystyrene-block-poly(acrylic acid) (PS-b-PAA), poly(ethylene oxide)-block-polylactide (PEO-b-PLA)). The addition of MUL-capped nanoparticles during the self-assembly process was found to stabilize colloidal polymer assemblies that otherwise tend to form macroscopic aggregates in water. Multicompartment polymersomes with complex internal membrane structures were formed at high nanoparticle volume percent, demonstrating that the interfacial assembly of nanoparticles can be used to create interesting new types of polymer assemblies while providing additional functionalities. This strategy offers a simple method for the formation of nanoparticle-loaded polymersomes that is applicable to various types of amphiphilic polymers.

Single cell synchrotron FT-IR microspectroscopy reveals a link between neutral lipid and storage carbohydrate fluxes in S. cerevisiae

In most organisms, storage lipids are packaged into specialized structures called lipid droplets. These contain a core of neutral lipids surrounded by a monolayer of phospholipids, and various proteins which vary depending on the species. Hydrophobic structural proteins stabilize the interface between the lipid core and aqueous cellular environment (perilipin family of proteins, apolipoproteins, oleosins). We developed a genetic approach using heterologous expression in Saccharomyces cerevisiae of the Arabidopsis thaliana lipid droplet oleosin and caleosin proteins AtOle1 and AtClo1. These transformed yeasts overaccumulate lipid droplets, leading to a specific increase in storage lipids. The phenotype of these cells was explored using synchrotron FT-IR microspectroscopy to investigate the dynamics of lipid storage and cellular carbon fluxes reflected as changes in spectral fingerprints. Multivariate statistical analysis of the data showed a clear effect on storage carbohydrates and more specifically, a decrease in glycogen in our modified strains. These observations were confirmed by biochemical quantification of the storage carbohydrates glycogen and trehalose. Our results demonstrate that neutral lipid and storage carbohydrate fluxes are tightly connected and co-regulated.

Integrated self-assembly of the Mms6 magnetosome protein to form an iron-responsive structure

A common feature of biomineralization proteins is their self-assembly to produce a surface consistent in size with the inorganic crystals that they produce. Mms6, a small protein of 60 amino acids from Magnetospirillum magneticum strain AMB-1 that promotes the in vitro growth of superparamagnetic magnetite nanocrystals, assembles in aqueous solution to form spherical micelles that could be visualized by TEM and AFM. The results reported here are consistent with the view that the N and C-terminal domains interact with each other within one polypeptide chain and across protein units in the assembly. From studies to determine the amino acid residues important for self-assembly, we identified the unique GL repeat in the N-terminal domain with additional contributions from amino acids in other positions, throughout the molecule. Analysis by CD spectroscopy identified a structural change in the iron-binding C-terminal domain in the presence of Fe³⁺. A change in the intrinsic fluorescence of tryptophan in the N-terminal domain showed that this structural change is transmitted through the protein. Thus, self-assembly of Mms6 involves an interlaced structure of intra- and inter-molecular interactions that results in a coordinated structural change in the protein assembly with iron binding.

Tunable nano-oleosomes derived from engineered Yarrowia lipolytica

Oleosomes are discrete organelles filled with neutral lipids surrounded by a protein-embedded phospholipid monolayer. Their simple yet robust structure, as well as their amenability to biological, chemical, and physical processing, can be exploited for various biotechnology applications. In this study, we report facile biosynthesis of functionalized oleosomes within oleaginous yeast Yarrowia lipolytica, through expression of oleosin fusion proteins. By fusing a cDNA clone of a sesame oleosin with either the coding sequence of a red fluorescent protein mCherry or a cellulosomal scaffolding protein cohesin from Clostridium cellulolyticum, these oleosin-fusion proteins were efficiently expressed and specifically targeted to and anchored on the surface of the oleosomes within the Y. lipolytica cells. The engineered oleosomes can be easily separated from the Y. lipolytica cell extract via floating centrifugation and both mCherry and cohesin domains are shown to be functional. Upon sonication, the engineered Yarrowia oleosomes exhibit a mean diameter of 200-300 nm and are found to be highly stable. The feasibility of co-displaying multiple proteins on the Yarrowia oleosomes was demonstrated by incubating cohesin-displaying oleosomes with different dockerin-fusion proteins. Based on this strategy, engineered oleosomes with both cell-targeting and reporting activities were created and shown to be functional. Taken together, the Yarrowia oleosome surface display system in which oleosin serves as an efficient membrane anchor motif shows great promise as a simple platform for creating tunable nanoparticles.

Integral Proteins in Plant Oil Bodies

Hydrophobic storage neutral lipids are stably preserved in specialized organelles termed oil bodies in the aqueous cytosolic compartment of plant cells via encapsulation with surfactant molecules including phospholipids and integral proteins. To date, three classes of integral proteins, termed oleosin, caleosin, and steroleosin, have been identified in oil bodies of angiosperm seeds. Proposed structures, targeting traffic routes, and biological functions of these three integral oil-body proteins were summarized and discussed. In the viewpoint of evolution, isoforms of oleosin and caleosin are found in oil bodies of pollens as well as those of more primitive species; moreover, caleosin- and steroleosin-like proteins are also present in other subcellular locations besides oil bodies. Technically, artificial oil bodies of structural stability similar to native ones were successfully constituted and seemed to serve as a useful tool for both basic research studies and biotechnological applications.

Towards an artificial cell

We are on the verge of producing "synthetic cells," or protocells, in which some, many or all of the tasks of a real biological cell are harnessed into a synthetic platform. Such advances are made possible through genetic engineering, microfabrication technologies, and the development of cellular membranes from new surfactants that extend beyond phospholipids in stability and chemical control, and can be used to introduce designer functionality into membranes and cells. We review some of the recent advances in the development of synthetic cells and suggest future exciting directions.